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Abstract
The enhanced global biodiesel production is also yielding increased quantities of glycerol as main coproduct. An effective application of glycerol, for example, as low-cost substrate for microbial growth in industrial fermentation processes to specific products will reduce the production costs for biodiesel. Our study focuses on the utilization of glycerol as a cheap carbon source during cultivation of the thermoplastic producing bacterium Ralstonia eutropha H16, and on the investigation of carbohydrate transport proteins involved herein. Seven open reading frames were identified in the genome of strain H16 to encode for putative proteins of the phosphoenolpyruvate-carbohydrate phosphotransferase system (PEP-PTS). Although the core components of PEP-PTS, enzyme I (ptsI) and histidine phosphocarrier protein (ptsH), are available in strain H16, a complete PTS-mediated carbohydrate transport is lacking. Growth experiments employing several PEP-PTS mutants indicate that the putative ptsMHI operon, comprising ptsM (a fructose-specific EIIA component of PTS), ptsH, and ptsI, is responsible for limited cell growth and reduced PHB accumulation (53%, w/w, less PHB than the wild type) of this strain in media containing glycerol as a sole carbon source. Otherwise, the deletion of gene H16_A0384 (ptsN, nitrogen regulatory EIIA component of PTS) seemed to largely compensate the effect of the deleted ptsMHI operon (49%, w/w, PHB). The involvement of the PTS homologous proteins on the utilization of the non-PTS sugar alcohol glycerol and its effect on cell growth as well as PHB and carbon metabolism of R. eutropha will be discussed.
Highlights
Biodiesel is currently beside ethanol the major renewable energy source for substitution of petroleum
The uptake of N-acetylglucosamine in R. eutropha is mediated by a sugar-specific phosphoenolpyruvate:carbohydrate phosphotransferase system (PTSNag consisting of EINag-HPrNag-EIIANag [nagF] and EIIBCNag [nagE]) that functions independently from the two general components of the bacterial phosphoenolpyruvate-carbohydrate phosphotransferase system (PEP-PTS), histidine phosphocarrier protein (HPr, ptsH) and enzyme I component (EI, ptsI)
Based on the results of previous studies (Krauße et al 2009,; Kaddor and Steinbüchel 2011) the genome of R. eutropha was investigated in silico for the occurrence of PEP-PTS homologous proteins
Summary
Biodiesel (fatty acid methyl esters) is currently beside ethanol the major renewable energy source for substitution of petroleum. The uptake of N-acetylglucosamine in R. eutropha is mediated by a sugar-specific phosphoenolpyruvate:carbohydrate phosphotransferase system (PTSNag consisting of EINag-HPrNag-EIIANag [nagF] and EIIBCNag [nagE]) that functions independently from the two general components of the bacterial PEP-PTS, histidine phosphocarrier protein (HPr, ptsH) and enzyme I component (EI, ptsI). The chromosomal context of each of these genes has already been described, and deletion mutants lacking combinations of genes involved in the PEP-PTS or/and fructose-specific ABC transport were previously generated (Kaddor and Steinbüchel 2011,). In addition to the general sugar import, the PEP-PTS exhibits regulatory cellular functions and may serve as a linkage between nitrogen and carbon metabolism (Reizer et al 1992,; Kotrba et al 2001,; Commichau et al 2006,; Velázquez et al 2007,; Pflüger and de Lorenzo 2008,; Krauße et al 2009). Besides the carbohydrate-related PEP-PTS, a paralogous nitrogen-related PTS (PTSNtr) exists in many Gram-negative bacteria whose regulatory functions, components and interactions with the PEP-PTS were extensively reviewed recently (Zimmer et al 2008,; Pflüger-Grau and Görke 2010)
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